The present invention relates to a fuel pump, specifically to a fuel pump applicable for a high pressure fuel pump for the direct gas injection system for automotive gasoline engines.
In the internal combustion engines, especially, automotive gasoline engines, the direct gas injection system has been studied in recent years for the purpose of the improvement of the fuel consumption performance, the reduction of the harmful exhaust gas and the improvement of the drive performance and the acceleration performance.
In the direction gas injection system, in order to inject directly gasoline into the cylinders of the internal combustion engine even when the compress ion stroke, a high pressure fuel pump which can supply gasoline with the high pressure, for example, more than 3 MPa is required.
In case of using gasoline for the lubrication of the drive part and the sealing of the rotor shaft of the fuel pump, as the viscosity of gasoline is extremely smaller than that of general purpose lubricating oil, the age of the rotational load support part of the drive part, especially, the age of the bearing becomes extremely short, and the reliability of the sealing mechanism of the rotor shaft becomes low.
In order to solve the above problem, as shown in Japanese Patent Laid Open No. 4-209981 (1992), what is known is the fuel pump in which the pressure-up of the fluid can be facilitated easily by using secondary fluid having higher viscosity and lubrication properties, and the operation fluid can be pressurized up by the piston through the bellows, as well as the lubrication of the load support part such as bearing is performed by the secondary fluid, and the sealing mechanism of the rotor shaft can be established by the secondary fluid.
However, as the number of pistons in the fuel pump described in Japanese Patent Application Laid-Open No. 4-209981 (1992) is only one, the pressure pulsation of the supplied fluid becomes larger. For the direct gas injection apparatus, it is required to establish the minimum fluctuation of the pressure of the supplied fuel with respect to the pressure control accuracy and response of the injected fuel and the flexible condition for the injection time selection. Although it is desirable to make the configuration of the piston multi-cylinder in order to make smaller the pressure pulsation, there has been such a problem that the size of the fuel pump is larger in the configuration that a bellows are placed for the individual piston as shown in Japanese Patent Application Laid-Open No. 4-209981 (1992).
An object of the present invention is to provide a fuel pump which has high reliabity and which is minitualized, and with small pressure pulsation by lubricating the drive part using lubricating fluid.
In order to attain the above object, the fuel pump of the present invention has a shaft for transmitting a driving force given outside; a swash plate rotated by the shaft; a wobble plate for converting revolution movement of the swash plate; a plurality of pistons reciprocating by wobble movement of the wobble plate; and a bulkhead for separating a fuel room and a drive room in a crank case for containing the swash plate, the wobble plate and the pistons, where with a configuration that a bearing for transmitting driving force between the shaft and the swash plate and a bearing for transmitting driving force between the swash plate and the wobble plate are placed in the drive room, those bearing are lubricated; and with a configuration that the plurality of pistons are placed in the fuel room, the fuel is intaken and discharged by the individual pistons.
With this configuration, a highly reliable and low pressure pulsation and small fuel pump can be obtained.
In the above described fuel pump, the bulkhead is configured with a bellows in which an inside of the bellows is supplied as a fuel room, and an outside of the bellows is supplied as a drive room. With this configuration, the leakage of the fuel can be protected.
According to another aspect of the present invention, the fuel pump has a shaft for transmitting a driving force given outside; a swash plate rotated by the shaft; a wobble plate for converting revolution movement of the swash plate; a plurality of pistons reciprocating by wobble movement of the wobble plate; and a bulkhead for separating a crank case composed of a front body and a cylinder block for containing the swash plate, the wobble plate and the pistons into two independent rooms, a part of the bulkhead being fixed at the wobble plate.
With this configuration, a highly reliable and low pressure pulsation and small-sized fuel pump can be obtained.
In the above described fuel pump, one of the two independent rooms separated by the bulkhead is supplied as a fuel room; and with a configuration that an inlet port and an inlet valve of the piston is placed in said fuel room, the fuel is directly supplied from the fuel room into a cylinder room of the piston.
In the above described fuel pump, a slipper is defined between the wobble plate and the piston, in which the contact surface of the slipper to the wobble plate is substantially a flat plane, and the contact surface of the slipper to the piston is a sphere; and the slipper has a channel connected to the inlet port of the piston and the connecting port connected to the channel on the plane surface of the slipper.